Electrical discharge lamp



May 23, 1933. c. e SMITH V ELECTRICAL DISCHARGE LAMP Filed April 24 Patented May 23, 1933 UNITED STATES PATENT OFFICE CHARLES G. SMITH, OF MEDFOBD, MASSACHUSETTS, ASSIGNOR TO RAYTHEON, INC., OF CAMBRIDGE, MASSACHUSETTS, A CORPORATION OF MASSACHUSETTS ELECTRICAL DISCHARGE LAMP a lication filed April 24,

This invention relates to electrical discharge lamps. Among the objects of this invention is to produce such a lamp which may be operated ata high current dens ty.

The foregoing and other ob ects Wlll be best understood from the following description of an exemplification of myinvention, reference being had to the. accompanying drawing whercin- Fig. l. is a cross-sectional view of the lightgenerating elementof my novel lamp; and

' creased by increasing the power input, by

decreasing the volume of the discharge space, by decreasing the cross-sectional area of the discharge space or by a combination of these three factors.

However, an increase in current density or intensity of the disclnirge causes a larger amount of heat to be liberated in the. discharge space. This heat tends to raise the temperature both of the atmosphere in which the discharge takes place and the walls of the. container which enclose the discharge. Since the walls of the container must .be transparent to light radiations, glass or quartz containers are used. These materials cannot be used above certain temperatures. Quartz, for example, becomes devitrified" above approximately 900 C and also becomes a fairly good conductor at that temperature. Pyrex glass has a tendency to soften above approximately 500. (1, and other kinds of glass soften. at temperatures considerably below 500. Thus the intensity of the discharge is limited by the temperatures at-which the containers may be operated.

In accordance with my inive'ntion I enable a discharge to be maintained at a high our- 1931. Serial No. 532,464.

rent density by preventing the temperature of the" container from rising to excessively high points. In the embodiment shown, for example, I place the container enclosing the discharge in an atmosphere having a high thermal conductivity and surround this atmosphere with a hermetically sealed transparent member having a large area, from which heat can be dissipated, with respect to the area of the container.

The lamp which I have shown consists of a container '1 which is preferably constructed of quartz, although various kinds of glass could he used. This container comprises a toroldal member 2 having legs 2' and 3 sealed thereon. By making the container in the form of a torus the cross-sectional area of the discl'iarge path for a given volume of dis charge space is decreased. Therefore I can obtain a greater density of current per unit of cross-sectional area with the same power input than if a container made in the form of a. globe were used. Moreover, the total surface of the container from which heat can bedissipated is greater than with a globe of like volume. However, in certain cases it may be desirable to have the container in the form of a globe. The walls of the container 1 are made quite thin in order to allow the heat generated within said container to pass readily through said walls. This container is thoroughly evacuated and the walls there of are freed of all occluded gases inaccordance with the usual practice.

Some material having the desired spectral properties is then introduced into the container 1. This material may be gases, for example, neon, helium or argon, or some easily vaporizable material, I for example, mercury, zinc or cadmium. When the easily Vaporizable materials are used, it is desirable, though not absolutely necessary, to also introduce into the container a rare gas, such as argon, or a mixture of rare'gases at a pressure of about one to two millimeters of mercury.

The container 1 is disposed within the glass envelope 10, having a re-entrant portion 11 and a press 12 of the usual construction. Supporting wires 15 and 16 are sealed in the press 12. These wires are engaged by metal bands 17 and 18 which encir 2' and 3 of the container. These bands 17 and 18 are fitted tightl around the legs 2' and 3 and wires 15 an 16 so that the container is supported firmly in osition. Wires 15 and 16 also serve as lea for high frequency currents from an oscillator 19 to a coil 20 concentric with the'toroidal member 2. This coil is preferably placed inside the torus in order to minimize its interference with the radiation of light from the container 1. The coil 20, however, may be disposed in any manner with relation to the container 1 as long as the toroidal member 2 is in inductive relation to the coil. The coil 20 comprises a few turns of wire which is highly polished in order to produce a reflecting surface thereon. Such reflecting surface cuts down the loss of light which falls upon the coil.

In order to conduct heat rapidly away from the walls of the container 1, the envelope 10 is filled with some material having a very high thermal conductivity. This malegs terialis preferably a gas and may consist of hydro en, helium or the like, or a mixture of suc gases. PreferablyI use a mixture of helium and hydrogen, the h drogen bein not more than about 25%. e pressure 0 the gas within the envelope 10 is sufliciently high so that an electrical discharge will not be induced-therein by the coil 20.

When the coil 20 is furnished with high frequency currents from the source 19, an electrical discharge will be induced in the atmosphere within the container.

The full voltage of the source 19 which is impressed on the bands 17 and 18 is'suificient to start a low discharge in the container. This glow discharge iomzes the gases in the torus and increases the conductivity so that the coil 20 can induce a rin discharge within the torus. Thus the ban s 17 and 18 also serve as starting electrodes. Upon the discharge occurring within the container 1 light having the characteristic spectral properties of the particular atmos here used will be emitted. The voltage 0 the source 19 to gether with the relative dimensions and constants of the coil 20 and container 1 are so chosen that the discharge within the container 1 is maintained at a very hi h current density and consequently a very igh eflicien'cy. I have found it advisable at the pressure mentioned not to have the diameter of the bore of the toroid shown less than about 4. However it is possible to use smaller bores by using higher pressures of the gas within the container and inducing higher voltages therein. Of course larger sizes of bore may also be used.

When an easily va orizable material and a rare gas is usedin t e container 1, the discharge initially starts in the rare gas. The

heat liberated, by this discharge causes the vaporizable material to be va orized whereupon the discharge is carried by the vapor due to the fact that it has a lower ionization voltage than that of the rare gas. In such case, the light emitted will have predominantly the spectral properties of the vapor.

The heat which is liberated by this intense discharge passes readily through the thin walls of the container 1. Due to the high thermal conductivity of the atmosphere surrounding the container 1, this heat is rapid- 1y transmitted through this atmosphere to t e outer container 10. This container having a relatively large area with respect to the area of the container 1 can dissipate to the outer atmosphere the total amount of heat firansmitted to it without becoming unduly When vapors are used as the source of light, the vapor pressure varies in accordance with the temperature of the coolest ortion of the vapor. It is advisable to keep the vapor ressure from rising to too high a value. Since the legs 2 and 3 are cooler than the other portions of the tube the vapor pressure will be determined by the temperature of the coolest portion of these legs. The temperature of these legs is determined by the temperature of the gases around them. Since the heat from these gases is rapidly dissipated from the comparatively large area of the container 1 these gases will be kept relatively cool. Thus even at the high intensity at which I operate my lamp the vapor pressure will not rise to excessive values. Since the atmosphere in the envelope 10 is non-oxidizing, the finish of coil 20 may be of any kind which will not tarnish in such an atmosphere. This finish may be, for example, highly polished silver or chromium.

The discharge will remain within the toroidal member 2 and will not occur within the atmosphere of the envelope 10 if certain conditions exist. For example, if helium alone is used, the Walls of the envelope 10 may be placed close to the walls of the lamp 1, and the helium in the restricted space so formed Will not allow a discharge to be initiated or maintained therein. However, since it is usually'advisable to have a rather large surface for the envelope 10 in order to increase the radiating surface, the pressure at which the helium is maintained is kept fairly high and is preferably in the neighborhood of one atmosphere. The addition of some hydrogen to the helium will enable the pressure within the envelope 10 to be maintained at a much lower value. I have found that a mixture of helium and hydrogen, the hydrogen being not more than about 25%, enables the presif released into the air so that any danger of, explosion due to the use of h drogen, is avoided. However, I do not wis to be limited to the use of hydrogen in this s ecific amount inasmuch as it is clear that by rogen alone could be used for the atmosphere with-- in the envelope 10, and prevent a discharge from taking place at low pressures.

The invention is not limited to the particular details of construction, materials, or processes described above, as many e u1va lents will suggest themselves to those s llled in the art.

It is accordingly desired that the appended claims be givena broad interpretation commensurate with the scope of the invention within the art.

What is claimed is:

1. I11 an electrical discharge device comprising a container, an atmosphere within said container in which an electrical discharge of high current density is adapted to be maintained, an envelope enclosing said container, said envelope being filled with a gas of high heat conductivity and having a heat dissipating outer surface substantially in excess of the heat dissipating surface of said container.

2. An electrical discharge lamp comprising a transparent vessel filled with a radiating gas, a transparent envelope enclosing said vessel, said envelope being filled with a gas of high heat conductivity and having a dissipating outer, surface substantially'in excess of the heat dissipating surface of said vessel.

3. An electrical discharge lamp comprising a transparent vessel filled with a radiating gas, a transparent envelope enclosing said vessel, said envelope being filled with a gas of high heat conductivity and having a heat dissipating outer surface substantially in excess of the heat dissipating surface of said vessel, and high frequency inducing means for inducing a discharge in the gas in said inner vessel.

4. An electrical discharge lamp comprising a transparent vessel filled with a radiating gas, a transparent envelo e enclosing said vessel, said envelope being lled with a gas of high heat conductivity and havin a heat dissipatingouter surface substantial y in excess of the heat dissipating surface of said vessel, and high frequency inducing means for inducing a discharge in the gas in said inner vessel, the pressure of the gas withinsaid envelope being of such a value that no discharge is induced therein.

5. An electrical dlscharge lamp comprising a vapor-filled transparent vessel, a trans-,

parent envelope enclosing said vessel and filled with a gas of high heat conductivity,v

said vessel having a discharge path in which an intense current flow is maintained developing substantial heat, said vessel also having a pocket disposed outside the path of the discharge and immersed in a relative cool section of the envelope to limit the pressure in said vessel.

6. An electrical discharge lamp comprise,

ing a toroidal transparent vessel filled with a radiating gas, a transparent envelope enclosing said vessel and filled with a gas of high heat conductivity, and high frequency 1n 8.. An electrical discharge lamp compris-' ing a transparent vessel filled with a radiating gas, a transparent envelope enclosing said vessel, said envelope bei-ng filled with helium and having a heat dissipating outer surface substantially in excess of the heat dissipating surface of said vessel. v

9. An electrical discharge lamp com rising a transparent vessel filled with a m iating gas, a transparent envelope enclosing said vessel, said envelope containin a mixture of helium and hydrogen, and having a heat dissipating outer surface substantially in excess of the heat dissipating surface of said vessel. 10. An electrical discharge lamp comprismg a transparent vessel filled with a radiating gas, high frequency inducing means for inducing a discharge in said gas, said means including a coil having a polished light-reflecting surface, a transparent envelope enclosing said vessel and filled with a gas inert with respect to the surface of said coil, said coil being placed outside of said vessel within said transparent envelope.

11. An electrical discharge lamp comprising a hermetically sealed vessel filled with a gas in which an electrical discharge is adapted to be maintained, means for rapidly conducting away the heat generated in said vessel, comprising a gas of high heat conductivity in which outer surfaces of said vessel are placed, and a hermetically sealed envelope enclosing said gas of high heat, conductivity.

12. An electrical discharge lamp comprising a transparent vessel filled with a radiating gas, a transparent envelope enclosing said vessel, said envelope being filled with a gas of high heat conductivity and having a heat dissipating outer surface substantially in excess of the heat dissipating surface of said vessel, high frequency inducing means for inducing a discharge in the gas in said inner vessel, the pressure of the gas within said envelope being of such a value that no discharge is induced therein, and means for increasing the permissible pressure of said latter gas comprising a quantity of hydrogen mixed therewith.

13. An electrical discharge lam comprising a transparent vessel filled wit a radiating gas, a transparent envelope enclosing said vessel, said envelope being filled with a gas of high heat conductivity and having a heat dissipating outer surface substantially in excess of the heat dissipating surface of said vessel, high frequency inducing means for inducing a discharge in the gas in said inner vessel, the pressure of the gas within said envelope being of such a value that no discharge-is induced therein, and means for increasing the permissible pressure of said latter gas comprising a quantity of hydrogen mixed therewith, the proportion of hydrogen being not in excess of twenty-five per cent,

14. A space discharge device comprising a hermetically sealed envelope, a gas In which an electrical discharge is adapted to take place within said envelope, a coil adapted to be supplied with high frequency currents for inducing currents in said gas and disposed in inductive relationship to said gas, two electrodes supported at points spaced apart on said container, and two leads for said coil, said leads being connected to sald electrodes and being adapted to be electrically connected to a source of high frequency current.

15. A space discharge device comprising a hermetically sealed envelope, a gas 1n which an electrical discharge is adapted to take place within said envelope, means for initiat-' ing a discharge in said gas comprising two electrodes supported at points spaced apart on said container, means for maintaining a discharge in said gas comprising a coil adapted to be supplied with high frequency currents for inducing currents in said gas and disposed in inductive relationship to said gas, and two leads for said coil, said leads being connected to said electrodes and being adapted to be electrically connected to a source of high frequency current.

16. A space discharge device comprising a hermetically sealed envelope, a gas In which an electrical discharge is adapted to take place within said envelope, a coil adapted to be supplied with high frequency currents for inducing currents in said gas and disposed in inductive relationship to said gas, two electrodes supported at points spaced apart on said container and external to said container, and two leads for said coil, said and means and a source of high frequency current connected to said lea 18. An electrical discharge lamp comprising a sealed vessel filled with a as in which an electrical discharge is adapte to be maintained, means for rapidly conducting away the heat generated in said vessel, comprising a gas of high heat conductivity in which the outer surfaces of said vessel are placed, and an envelope enclosing said gas of high heat conductivlty.

19. An electrical discharge lamp comprising a sealed vessel filled with a as in which an electrical discharge isadapte to be maintained, means for rapidl conducting away the heat 1generated in sai vessel, comprising a gas of igh heat conductivity in which the outer surfaces of said vessel are placed, an envelope enclosing said gas of high heat conductivity, means for producing a discharge in the gas in said inner vessel, conducting leads extendin through said gas of high heat conductivity to said last-named means, for preventing a discharge through said gas of high heat conductivity between said conducting leads.

20. An electrical discharge lamp comprising a transparent vessel filled with a radiating gas, and inductive means for inducing a discharge in said gas, said means including a coil having a polished light-reflecting surface, said coil being placed in inductive relationship with respect to said radiating gas.

In testimony whereof, I have si ed my name to this specification, this 23rd day of April, 1931.

- CHARLES e. SMITH.

electrodes and said leads being electrically I connected and clamped to said container at said spaced points.

17 An induction lamp comprising a transparent container, a coil adapted to be sup plied with high frequency currents for exciting said lamp and disposed adjacent said lamp, two electrodes supported by said container at points spaced apart from each other, a pair of leads for said coil, said leads being clamped to said container by said electrodes, 

